We are continuing to investigate the role of phospholipid-\and Ca2+-dependent protein kinase (protein kinase C) in the maturation of leukemia cells into macrophages. Data generated over the past year in many laboratories, including our own, confirm the hypothesis put forth in our original application: protein kinase C is the phorbol diester receptor. We have synthesized chemically defined diacylglycerols and shown them to be the "endogenous phorbols" as evidenced by their ability to: (1)\activate protein kinase C; (2)\competitively inhibit radiolabeled phorbol diester binding to the soluble or cellular phorbol diester receptor; (3)\induce leukemic cells to differentiate into macrophages; and (4)\mimic phorbol diester-induced phosphoprotein changes that occur during macrophage differentiation. Biologically active phorbol diesters and cell-permeable diacylglycerols induce phosphorylation of proteins with Mr = 21, 52, 65, and 80 kilodaltons in 32P-loaded HL-60 cells. This year, emphasis will be placed on purification of protein kinase C from HL-60 cells and antibody production. The major phosphoproteins will be purified and 32P amino acids and peptide maps determined. The long-term objective of this project is to begin to understand myeloid maturation at a biochemical level. The major scientific disciplines involved are hematology, oncology, and cell biology. In vitro maturation of promyelocytic leukemia cells serves as a model for bone marrow differentiation. Studies such as these may define the molecular defect which leads to cessation of myeloid maturation and hence, leukemia. The investigation is health-related because it explores a molecular pathway of differentiation which is blocked in leukemia. Agents active as inducers of cell maturation will soon find clinical application in the experimental treatment of leukemia and other malignancies. (B)